1. Field of the Invention
The present invention relates to the preparation of strontium nitrate by the reaction of strontium sulfate with calcium nitrate.
2. Description of the Prior Art
Strontium nitrate, which finds principal use in pyrotechnic applications for its red-colored flame, is typically derived from celestite, a strontium sulfate-containing ore.
In the most direct commercial manufacturing method, celestite ore is heated with an aqueous soda ash (sodium carbonate) solution to yield strontium carbonate as a precipitate. The separated strontium carbonate is reacted with aqueous nitric acid to form strontium nitrate, which is recovered by crystallization.
Strontium nitrate may alternatively be obtained from celestite ore via the "black ash" process, in which celestite is reduced to strontium sulfide black ash by heating with coal. The strontium sulfide is leached from the black ash with water, reacted with soda ash to form strontium carbonate, and the separated strontium carbonate treated with aqueous nitric acid to yield strontium nitrate.
A drawback to these and other similar processes is the multiple reaction steps and reactant materials required to produce strontium nitrate from the strontium sulfate-containing celestite ore.
U.S. Pat. No. 2,158,162 teaches that strontium nitrate may be obtained from celestite by boiling the latter in an aqueous barium nitrate solution. Barium sulfate precipitates from the aqueous reaction medium, leaving a solution from which strontium nitrate may be crystallized. A disadvantage of this technique is its dependence on barium nitrate as a reactant.
U.S. Pat. No. 2,030,659 teaches a single-reaction technique for converting barium or strontium sulfate to the corresponding nitrate (or chloride) by reaction with calcium nitrate (or chloride). Because the reaction is readily reversible, the reaction is first driven to completion by use of concentrated reactant solutions, and the reaction product is then extracted with a suitable organic solvent. The organic solvent is then evaporated to recover the extracted product.
It has been discovered that strontium nitrate may be obtained from celestite in a single-reaction process while nevertheless avoiding the drawbacks associated with the use of an organic solvent extractant for recovering the strontium nitrate product from the reaction medium.